The Contiki build system

The Contiki build system is designed to make it easy to compile
Contiki applications for different hardware platforms or into a
simulation platform by simply supplying different parameters to the
make command, without having to edit makefiles or modify the
application code.

The file example project in examples/hello-world/ shows how the
Contiki build system works. The hello-world.c application can be built
into a complete Contiki system by running make in the
examples/hello-world/ directory. Running make without parameters will
build a Contiki system using the native target. The native target is a
special Contiki platform that builds an entire Contiki system as a
program that runs on the development system. After compiling the
application for the native target it is possible to run the Contiki
system with the application by running the file hello-world.native. To
compile the application and a Contiki system for the ESB platform" the
command make TARGET=esb is used. This produces a hello-world.esb file
that can be loaded into an ESB board.

To compile the hello-world application into a stand-alone executable
that can be loaded into a running Contiki system, the command make
hello-world.ce is used. To build an executable file for the ESB
platform, make TARGET=esb hello-world.ce is run.

To avoid having to type TARGET= every time make is run, it is possible
to run make TARGET=esb savetarget to save the selected target as the
default target platform for subsequent invocations of make. A file
called Makefile.target containing the currently saved target is saved
in the project's directory.  Makefiles used in the Contiki build
system The Contiki build system is composed of a number of
Makefiles. These are:

    * Makefile: the project's makefile, located in the project directory.

    * Makefile.include: the system-wide Contiki makefile, located in
      the root of the Contiki source tree.

    * Makefile.$(TARGET) (where $(TARGET) is the name of the platform
      that is currently being built): rules for the specific platform,
      located in the platform's subdirectory in the platform/
      directory.
    
    * Makefile.$(CPU) (where $(CPU) is the name of the CPU or
      microcontroller architecture used on the platform for which
      Contiki is built): rules for the CPU architecture, located in
      the CPU architecture's subdirectory in the cpu/ directory.
    
    * Makefile.$(APP) (where $(APP) is the name of an application in
      the apps/ directory): rules for applications in the apps/
      directories. Each application has its own makefile.
    
The Makefile in the project's directory is intentionally simple. It
specifies where the Contiki source code resides in the system and
includes the system-wide Makefile, Makefile.include. The project's
makefile can also define in the APPS variable a list of applications
from the apps/ directory that should be included in the Contiki
system. The Makefile used in the hello-world example project looks
like this:

CONTIKI = ../..
all: hello-world
include $(CONTIKI)/Makefile.include

First, the location of the Contiki source code tree is given by
defining the CONTIKI variable. Next, the name of the application is
defined. Finally, the system-wide Makefile.include is included.

The Makefile.include contains definitions of the C files of the core
Contiki system. Makefile.include always reside in the root of the
Contiki source tree. When make is run, Makefile.include includes the
Makefile.$(TARGET) as well as all makefiles for the applications in
the APPS list (which is specified by the project's Makefile).

Makefile.$(TARGET), which is located in the platform/$(TARGET)/
directory, contains the list of C files that the platform adds to the
Contiki system. This list is defined by the CONTIKI_TARGET_SOURCEFILES
variable. The Makefile.$(TARGET) also includes the Makefile.$(CPU)
from the cpu/$(CPU)/ directory.

The Makefile.$(CPU) typically contains definitions for the C compiler
used for the particular CPU. If multiple C compilers are used, the
Makefile.$(CPU) can either contain a conditional expression that
allows different C compilers to be defined, or it can be completely
overridden by the platform specific makefile Makefile.$(TARGET).
